Active Presence Detection with Depth Sensing

1. A computer-implemented method for monitoring an operator's use of a secure system, the method comprising: (a) defining a detection zone extending from an operator terminal of the secure system to a depth boundary spaced apart from the operator terminal and corresponding to a distance from the operator terminal beyond which an operator cannot interact with the secure system; (b) using a depth-sensing camera system co-located with the operator terminal to acquire a series of images of one or more objects within the detection zone; (c) using the depth-sensing camera to measure distances from the operator terminal to the one or more objects in the series of images; (d) determining whether any of the one or more objects within the detection zone is a face, and, if so, associating the face with an operator; (e) following association of a detected face with the operator, using the depthsensing camera to track the distance from the operator terminal to the detected face and, if the distance extends beyond the depth boundary, signaling a walk-away event; and wherein step (d) comprises identifying, among a plurality of faces present within the detection zone, the face closest to the secure system based on distances to the plurality of faces measured using the depth-sensing camera and computationally associating that face with the operator.

2. A computer-implemented method for monitoring an operator's use of a secure system, the method comprising: (a) defining a detection zone extending from an operator terminal of the secure system to a depth boundary spaced apart from the operator terminal and corresponding to a distance from the operator terminal beyond which an operator cannot interact with the secure system; (b) using a depth-sensing camera system co-located with the operator terminal to acquire a series of images of one or more objects within the detection zone; (c) using the depth-sensing camera to measure distances from the operator terminal to the one or more objects in the series of images; (d) determining whether any of the one or more objects within the detection zone is a face, and, if so, associating the face with an operator; (e) following association of a detected face with the operator, using the depthsensing camera to track the distance from the operator terminal to the detected face and, if the distance extends beyond the depth boundary, signaling a walk-away event; and wherein step (d) comprises analyzing relative depth information measured with the depth-sensing camera to discriminate between faces and two-dimensional images thereof.

3. A computer-implemented method for monitoring an operator's use of a secure system, the method comprising: (a) defining a detection zone extending from an operator terminal of the secure system to a depth boundary spaced apart from the operator terminal and corresponding to a distance from the operator terminal beyond which an operator cannot interact with the secure system; (b) using a depth-sensing camera system co-located with the operator terminal to acquire a series of images of one or more objects within the detection zone; (c) using the depth-sensing camera to measure distances from the operator terminal to the one or more objects in the series of images; (d) determining whether any of the one or more objects within the detection zone is a face, and, if so, associating the face with an operator; (e) following association of a detected face with the operator, using the depthsensing camera to track the distance from the operator terminal to the detected face and, if the distance extends beyond the depth boundary, signaling a walk-away event; and wherein step (e) comprises tracking a collection of trackable key features associated with the operator between the successive images based, at least in part, on distances associated therewith.

4. The method of claim 3 , wherein tracking the key features comprises matching the key features between the successive images based at least in part on the distances associated therewith.

5. The method of claim 3 , wherein tracking the key features comprises filtering identified matches of key features between the successive images based at least in part on the distances associated therewith.

6. A computer-implemented method for monitoring an operator's use of a secure system, the method comprising: (a) defining a detection zone extending from an operator terminal of the secure system to a depth boundary spaced apart from the operator terminal and corresponding to a distance from the operator terminal beyond which an operator cannot interact with the secure system; (b) using a depth-sensing camera system co-located with the operator terminal to acquire a series of images of one or more objects within the detection zone; (c) using the depth-sensing camera to measure distances from the operator terminal to the one or more objects in the series of images; (d) determining whether any of the one or more objects within the detection zone is a face, and, if so, associating the face with an operator; (e) following association of a detected face with the operator, using the depthsensing camera to track the distance from the operator terminal to the detected face and, if the distance extends beyond the depth boundary, signaling a walk-away event; and wherein step (e) further comprises periodically restarting the tracking based on at least one of re-detection of the face or detection of a headshoulder portion associated with the operator, the at least one of re-detection of the face or detection of the head-shoulder portion being based at least in part on the distances measured using the depth-sensing camera.

7. The method of claim 6 , further comprising, repeatedly upon re-detection of the face, saving a face template for subsequent use during re-authentication.

8. The method of claim 7 , further comprising indexing the face templates based, at least in part, on face posture as determined from three-dimensional information contained therein.

9. An access-control system for monitoring an operator's use of a secure system, comprising: a depth-sensing camera system co-located with an operator terminal of the secure system; and a computational facility including a processor and associated memory, the memory storing instructions, for execution by the processor, for: (i) defining a detection zone extending from the operator terminal to a depth boundary spaced apart from the operator terminal and corresponding to a distance from the operator terminal beyond which an operator cannot interact with the secure system; (ii) analyzing images of one or more objects acquired by the depth-sensing camera to determine whether any of the one or more objects within the detection zone is a face, and, if so, associating the face with an operator; and (iii) following association of a detected face with the operator, tracking a distance from the operator terminal to the detected face using distance information acquired by the depth-sensing camera and, if the distance extends beyond the depth boundary, signaling a walk-away event.

10. The system of claim 9 , wherein the instructions stored in the memory comprise instructions for using the distance information acquired by the depth-sensing camera to discriminate between the operator and background objects present in the images.

11. The system of claim 9 , wherein the instructions stored in the memory comprise (i) a face-finding algorithm for first detecting faces in the images and (ii) instructions for thereafter computationally determining, using distance information acquired by the depth-sensing camera, which, if any, of the detected faces are present within the detection zone.

12. The system of claim 9 , wherein the instructions stored in the memory comprise a face-finding algorithm using distance information acquired by the depth-sensing camera for detecting faces only within portions of the image corresponding to the detection zone.

13. The system of claim 9 , wherein the instructions stored in the memory comprise instructions for, using distance information acquired by the depth-sensing camera, identifying, among a plurality of faces present within the detection zone, the face closest to the secure system and computationally associating that face with the operator.

14. The system of claim 9 , wherein the instructions stored in the memory comprise a spoof filter that analyzes relative depth information acquired by the depth-sensing camera to discriminate between faces and two-dimensional images thereof.

15. The system of claim 9 , wherein the instructions stored in the memory comprise instructions for tracking a collection of trackable key features associated with the operator between successive images based, at least in part, on distances associated therewith.

16. The system of claim 15 , wherein the instructions for tracking the collection of trackable key features comprises at least one of instructions for matching the key features between the successive images based at least in part on the distances associated therewith, or instructions for filtering identified matches of key features between the successive images based at least in part on the distances associated therewith.

17. The system of claim 9 , wherein the instructions stored in the memory comprise instructions for periodically restarting the tracking based on at least one of depth-based re-detection of the face or detection of a head-shoulder portion associated with the operator.

18. The system of claim 9 , further comprising a database storing face templates indexed based, at least in part, on face posture as determined from three-dimensional information contained therein.

19. The system of claim 18 , wherein the instructions stored in the memory further comprise an authentication application for authenticating the operator based on the associated detected face and the database.